Multivoice circuitry with vibrato for electronic musical instrument

ABSTRACT

A sinusoidal waveform signal of audiofrequency is clipped at one or more amplitude levels to establish a plurality of signal components. Any one of the signal components, the combination of two signal components algebraically added, or the combination of three signal components algebraically added produce resultant output signals having different waveform characteristics providing selectable multivoice musical tones simulating such instruments as the flute, diapason, horn, woodwind, or full organ. The original sinusoidal signal is generated by a resonant feedback oscillator having a bias that may be varied to produce a vibrato effect in the resultant signals. Signal selection is made by a switch assembly combining different paths including a phase inverter, through which clipped signal components are conducted. The various oscillators and the phase inverter may be transistorized.

United States Patent [72] Inventor John W. Padalino Morris Plains, NJ. [21] Appl. No. 829,472 [22] Filed June 2,1969 [45] Patented Jai. 12, 1971 [73] Assignee Whippany Electronics, Inc. a corporation of New Jersey [54] MULTIVOICE CIRCUITRY WITH VIBRATO FOR ELECTRONIC MUSICAL INSTRUMENT 21 Claims, 4 Drawing Figs.

[52] U.S.Cl 84/1.19, 84/ 1 .25 [51] Int. Cl G10hl/02, G10h 1/06 [50] Field ofSearch 84/101,

1.05,1.111.13,l.19,1.21,1.22,1.24,1.25, 1.27, (E, FB)

[56] References Cited UNITED STATES PATENTS 3,049,957 8/1962 Meyer 84/].24

Freq. Controls Audia Freq. 1 0st.- and Clipper 3,063,324 11/1962 Campbell 84/1.01 3,097,253 7/1963 Peterson 84/122 3,433,880 3/1969 Southard 84/1.17

Primary ExaminerW. E. Ray AttorneysClarence A. OBrien and Harvey B. Jacobson ABSTRACT: A sinusoidal waveform signal of audiofrequency is clipped at one or more amplitude levels to establish a plurality of signal components. Any one of the signal components, the combination of two signal components algebraically added, or the combination of three signal components algebraically added produce resultant output signals having different waveform characteristics providing selectable multivoice musical tones simulating such instruments as the flute, diapason, horn, woodwind, or full organ. The original sinusoidal signal is generated by a resonant feedback oscillator having a bias that may be varied to produce a vibrato effect in the resultant signals. Signal selection is made by a switch assembly combining different paths including a phase inverter, through which clipped signal components are conducted. The various oscillators and the phase inverter may be transistorized.

Control A ssembly Phase 8 22 Inverler j Swift/r Control ing audio signals and more particularly to the production of selected musical tones by electronic means. v

The use of audiofrequency oscillators for sine wave generators and waveform shaping circuits to .produce audiofrequency tones simulating different instruments, is well known. Generally, a separate wave shaping circuit section is required for each musical instrument to be simulated. An important object of the present invention therefore is to provide a waveform generator through which audiofrequency signals having difierent waveform characteristics may be produced from a sine wave signal to thereby electronically simplify the generator and make operation thereof more reliable.

In accordance with the present invention, an audiofrequency oscillator of the resonant feedback type is utilized to generate a sine wave at a selected frequency. The output of the oscillatoris conducted through three different paths by a signal clipping network. The sine wave is clipped at a positive and negative level to divide it into three components respectively conducted alongthe three signal transmitting paths to an attenuator and switch assembly'through which waveform characteristics are selected. By varying the bias applied to the oscillator, the voltage levels at which the sine wave signal is clipped may be cyclically changed to produce a vibrato effect. The three different paths through which the clipped signal clipped portion transmitted to path 16 is reduced to less than 160 as shown by signal pulse 38 in FIG. 2. The negative portion of the sinusoidal waveform conducted through path 20 will then be more than l60 as shown by 40' while the intermediate portion will have a different duty cycle ratio than that associated with squared waveform portion 42. By varying the bias and the output angle of conduction continuously, the squared waveform may be changed to a small conducting pulse 42. r

The three basic clipped signal components 38 (A), 42 (B) and 40 (C) are fed to the switch assembly 22 so that one, two or all three of the signal components may be selectively attenuated and "transmitted to one of the .two output paths 24 and 26, producing a resultant signal in path 30 which is the algebraic sum of in phase and phase shifted clipped signal components. FIG. 2 shows some examples of such resultant waveforms. Waveform 44 (A-C) is the algebraic sum of clipped signal component 38 and clipped signal component 40 phase shifted 180 by the phase inverter 28. Signal component 42 is phase shifted 180 relative to signal components 38 and 40 all of which are algebraically added to produce the resultant wave form 46 (A-B+C). Phase shifted signal comcomponentsare conducted, are combined in different combinations through the selector switch assembly and fed to two output paths. One of the output paths conducts signals through a phase inverter to cause a phase shift of 180 before the signal components are algebraically added to form a selected output wave form. These. together with other objects and advantages which will become subsequently apparent residein the details ofconstruction and operation as more fully hereinafter. described and claimed, reference being had ;to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which: I Y

* FIG. I is a schematic block diagram illustrating the principles underlying thepresent invention.

FIG. 2 is 'a graphic illustration of the signals produced in accordance with the apparatus of the present invention.

FIG. 3 is a simplified electrical circuit diagram illustrating the basic features of the present invention.

FIG. 4 is an electrical circuit diagram illustrating a specific embodiment of the present invention.

Referring now to the drawings in detail, FIG. 1 schematically illustrates the basic features of the apparatus forming the present invention, generally referred to by reference numeral 10. The apparatus includes an oscillator 12 from which a continuous sinusoidal wave form signal is fed to a clipper network 14. The original signal is divided amongst three signal transmitting paths 16, 18 and 20 and fed to an attenuator and switch assembly 22. Two output signal conducting paths 24 and 26 emerge from the switch assembly. The clipped signal components conducted through path 26 pass through a phase inverter 28 to phase shift the same 180 relative to the signal components transmitted through path '24. The signal components are then algebraically added to produce a resultant signal in path 30 having a selected waveform characteristic.

'The resultant wavefonns produced by the apparatus of the present invention are particularly suited for musical organ tones. These tones originate from the aforementioned sinusoidal waveform referred to as 32 in' FIG. 2. The clipping circuit 14, with no bias applied, is operative to clip the signal 32 at a positive level 34 and a' negative level 36. A.clipped signal component 38 as shown in FIG. -2 having a conduction angle of about 160, will then appear as a pulse conducted through path 16 while a negative-type pulse 40 is conducted through path 20. The middle part of the sine wave 32 appears as a square waveform 42 conducted through the path 18. If

positive bias is applied to the clipping circuit 14 through bias control 44 as shown in FIG. 1, the conductive phase for the ponent 42. on the other hand is added only to signal com- 48 will appear as waveform 48'. The foregoing is merely exemplary of the many combinations and waveform characteristics that may be produced inaccordance with the present invention by multilevel clipping of a sinusoidal waveform and recombining clipped portions.

As shown in FIG. 3 bias may be continuously applied to the audiofrequency oscillator 12 at a vibrato rate from a bias vary ing control oscillator 54. An output tone is thereby produced whose harmonic content or timber varies at a rate determined by the frequency of the oscillator 54. The bias applied to the output of the oscillator 12 establishes the voltage levels 34 and 36 at which the sine wave output of the oscillator is clipped. The sine wave output is fed through the coupling capacitor 56 and coupling resistor 58 to the clipping circuit 14 which includes a signal transmitting resistor 60 establishing the path 18 for the signal component 42 and a pair of clipping diodes 62 and 64 connected in parallel with the resistor 60 for establishing the signal transmitting paths 16 .and 20 conducting signal components 38 and 40 respectively. A bias may be applied to established at the positive terminal of the charge storing capacitor 72. Thus,-the clipping diodes 62 and 64 may act as series elements shunted by resistors 68 and 70 to clip and transmit the positive and negative portions 38 and 40 of the sine wave signal at levels determined by the resistance values of the bias resistors. The clipping diodes may also act as shunts for the resistor 60 to clip the positive and negative portions from the sine wave signal and transmit the center squared portion thereof through the resistor 60.

The positive and negative clipped portions of the sine wave signal areselectively combined or individually fed through the switch assembly 66 and a'signal coupling capacitor 74 as shown in FIG. 3 to the emitter of NPN type, phase inverting transistor 76, the emitter being connected above ground by the emitter resistor 78. Thus, the signal component supplied to the emitter of transistor 76 will produce a corresponding, inphase output at the collector. Bias is applied to the base of transistor 76 through the voltage dividing resistors 80 and 82 so as to render the same conductive when the signal components are transmitted thereto by resistor 60 through the signal coupling capacitor 84. The transistor 76 being connected in a common emitter arrangement, will amplify the signal input to its base, phase shifted Thus, when signals are simultaneously fed through the capacitors 74 and 84 to the transistor, a resultant signal is transmitted from the collector to the signal coupling capacitor 86 which is the algebraic sum of the in-phase signal from capacitor 74 and the phase shifted signal passed by capacitor 84. The'gain of the signals transmitted through transistor 76 from path 16, 18 or 20 may be regulated by an attenuator including switch 50 and grounded resistor 52. l

One specific waveform generator circuit is illustrated in FIG. 4 which includes a plurality of audiofrequency oscillators 12, 12' etc. Frequency selecting controls 88. are associated with each of the oscillators. The controls 88 include a plurality of frequency selecting switches 90 connected to the ground line 92 and adapted to be momentarily closed, for example, by an organ player through a keyboard arrangement. Closing of a selected switch 90 grounds one of the series connected resistors 92 and thereby selects the output frequency of the associated oscillator. l

Power is supplied to each oscillator through a resistor 94 connected by conductor 96 and a voltage reducing resistor 98 to positive output terminal 100 of a power supplying rectifier which includes a rectifier diode 102 connected in series with the secondary winding of a power transformer 104 and a filter capacitor 106 connected between the output terminal 100 and the opposite terminal of the transformer secondary. The rectifier includes a second filter capacitor 108 connecting the transformer secondary to a lower potential output terminal 110 connected by voltage reducing resistor 112 to the output terminal 100. The primary winding of the transformer 104 is connected to an available AC voltage source upon closing of the power switch 114.

Thus, upon closing of the power switch 114, a DC source of voltage is established for powering the audiofrequency oscillators as well as the other components of the generator. This DC power supply forms part of a control assembly which also includes a grounded potentiometer 116 operatively connected with power switch 114. The resultant output signal of the waveform generator at an adjusted volume level is fed from the potentiometer through an amplifier 117 to a speaker 118. Also associated with the control assembly, is a potentiometer 120 controlling the volume level of a bass frequency signal. The bass frequency signal is derived from an oscillator 124 having a frequency control 200. The bass frequency signal is supplied from the oscillator 124 to an attenuating potentiometer 120. Thus, the bass frequency signal may be superimposed upon the resultant output signal from the phase shifting transistor 76 aforementioned and fed to the base of the amplifier transistor 136 through signal coupling capacitor 138. The amplified output signal at the collector of amplifier transistor 136 is fed to the output line 122 through signal coupling capacitor 140. Forward bias is maintained on the base of transistor 136 through the voltage dividing resistors 142 and 144 connected between potential point 110 of the DC power supply and ground. The positive potential point 110 is also connected to the load resistors 146 and 148 establishing bias for the collectors of transistors 76 and 136. Thus, the phase inverting transistor 76 hereinbefore described, in addition to performing a phase shifting function, also acts as a single stage driver for the output amplifier transistor 132.

With continued reference to FIG. 4 it will be observed that each of the audiofrequency oscillators 12, 12', etc. includes a NPN type transistor 150 having a grounded emitter and an output collector connected to the output signal coupling capacitor 56 and a source of DC bias from resistor 94. Base bias is established by adjustable resistor 152 in series with resistors 154, 158 and 166 connected between the forward bias supply and ground. Resistors 158 and 166 are shunted by capacitor 156 while the base is connected to the juncture between resistors 158 and 166. The forward bias on the base may be positively varied varied at a vibrato rate by a signal supplied to the base through resistor 168 connected by conductor 170 to the potentiometer 44 through which the output level of the vibrato signal oscillator 54 is varied. This causes negative shift in the signal level to change the levels at which the sine wave signal is clipped.

A filter capacitor 160 is connected between the collector and emitter of transistor 150 while series connected capacitors 162 and 164 interconnect the collector and base to form a resonant feedback path. Upon closingofone of the frequency selecting switches 90, the resonant feedback circuit is rendered operative at a selected frequency to produce a sine wave output at the collector of transistor 150. Since the transistor is arranged in a common emitter'config'uration, a signal phase shift occurs between the base and collector. The feedback circuit introduces an additional phase shift to make the feedback signal from the collector'to the base positive. Thus, a change in base current results in an amplified change in collector current phase shifted 180. The signal returned to the base through feedback capacitors 162 and 164 is inverted 180 to make it regenerative. The requisite phase shift occurs however at the frequency determined by the number of resistors 92 connected in series to ground.

The vibrato producing oscillator 54 is similar to the audiofrequency oscillators and accordingly includes a NPN type transistor 170 having an output collector connected to the potentiometer 44 through the signal coupling capacitor 172 and the resistor 174. Collector bias is supplied to the transistor 170 from the DC voltage source through resistor 176. The emitter is connected to ground through resistor 178 while base bias is established by adjustable resistor 180, resistor 182; re-. sistor 184, and resistor 186. A resonant feedback circuit interconnects the collector and base and includes feedback capacitors 188, and 192 and ground resistor 194 establishing the output frequency of the oscillator.

The bass frequency oscillator 124 isalso of the resonant feedback type and includes NPN type transistor 196 having an output collector connected to the positive voltage line 96 and to the potentiometer 120 through resistor 198. Base bias for the transistor is established by the resistors 200, 202, 204 and 206. The output frequency of the oscillator 124 is selectively established by the frequency controls 128 associated with the. resonant feedback circuit which includes the filter capacitors, 208, 210 and 212 connected between the collector and the base of the transistor 196. v

Each of the oscillators 12, 12', etc., is provided with a clipping circuit 14 hereinbefore described in connection with FIG. 3. Thus, three clipped signal components are fed from.

each clipping circuit to the switch assembly 22 thrdug'hrthe common signal transmitting lines 16, 18 and 20. An RC filter network 219 including capacitor 214, the input and output terminals of which are shunted through grounded resistors 216 and 218, couple the signal transmittinglines 16 and 20 to two of the input terminals 220 and 222 of the switch assembly 66, the third input terminal 224 being-directly connected to the signal transmitting line 18. The signal transmitting line 18 is interconnected with the output signal line 24 or 26 through series connected switches 226 and 228 and a bypass jumper for switch 50. The signal transmitting line 16 is interconnected through its RC coupling network 219 and terminal 220 with the output signal line 26 through switch 234 in the switch assembly. Finally, the signal transmitting line 20 .is interconnected with the output signal line 24 or 26 through its RC coupling network 219 and the switches 236, 238 and 50 or 240 within the switch assembly. A

The switches 226 and 236 are ganged and simultaneously displaceable from the operative position shown in FIG. 4 by means of a pushbutton control 242 arranged to select the waveform characteristics simulating a flute. A diapason pushbutton control 244 is interconnected with the switch 228 while a horn pushbutton control 246 is connected to the switch 238. The switches 234 and 240 are ganged and interconnected with a woodwind pushbutton control 248 and a full organ pushbutton control 250 is connected to the switch 50. When the switches 234 and 50 are displaced from the operative positions shown in FIG. 4, they engage contacts connected to ground through resistors 252 and 52.

In order to change the level of the bias applied to the signals passed through the switch assembly 66, a positive DC voltage line 256 connects the output terminal 110 of the power supply through resistor 258 to a switch 260 ganged with the switch 228 and through resistor 262 in series with resistor 258 to switches 264 and 266 respectively ganged with the switches 238 and 50..Thus, upon closing of any one of the switches 260, 264 and 266, a positive potential is applied through the resistors 68 and 70 to the signal transmitting lines 16 and 20.

When the control 242 is actuated, signal transmitting line 18 is disconnected from the output signal line 24 and connected to input terminal 220 and the output signal line 26. At

the same time, switch 236 is displaced to an inoperative position disconnecting the signal transmitting path 20 from the circuit. Thus, a resultant output signal is produced which represents a sine wave with the negative peak portions clipped therefrom to simulate a flute.

When the control 244 is actuated, the switch 228 is displaced from its operative position so as to disconnect the signal transmitting path 18 from the circuit and at the same time switch 260 is closed in order to add DC bias to the signal components transmitted through the paths 16 and 20. Thus, in the case of the controls 242 and 244, two in-phase signals are added to form the resultant output waveform simulating a diapason quality tone. in the case of control 244, bias is added whereas in the case of control 242, no bias is added tothe signal components.

When the control 246 is actuated, the switch 238 combines the signals transmitted through paths l8 and 20 and feeds them to output line 24 to be phase shifted. Bias is added to the signal component conducted through path 16 on the other hand by closing of the switch 264 and fed to output line 26. Thus, a combination of signals conducted through paths 18 and 20 are phase inverted and algebraically added to the signal conducted through path 16 to produce the resultant output waveform simulating the tones of a horn.

The tones of a woodwind are simulated by actuating the control 248 thereby disconnecting the signal paths l6 and 20 from the circuit through switches 234 and 240 and connecting the output line 26 to ground through resistor 252. The signal component 42 hereinbefore referred to in connection with FIG. 2 will then be produced as the output waveform. For full organ tone, the control 250 is actuated so that the signal com ponents conducted through paths 16 and 20 are biased through switch 266 while switch 50 connects the signal transmitting path 18 to ground through resistor 52, for attenuation of the signal transmitted from path 16 reducing its gain. The signal components conducted through paths l6 and 20-are combined and fed to the output line 26. The signal component being conducted through path 18 is phase inverted and then algebraically added to the other two in-phase signal components. When none of the described controls are actuated, the three signal components are combined as described in connection with actuation of control 250 except that they are not attenuated in order to simulate the musical tones of a reed instrument.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur tothose skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

lclaim:

1. A signal producing apparatus comprising means for generating a continuous signal, signal clipping means connected to said generating means for dividing the continuous signal into separate signal portions, and selectively controlled means connected to the signal clipping means for recombining different combinations of said signal portions establishing resultant signals which are different from the continuous signalv 2. The combination of claim 1 wherein said continuous signal is a sinusoidal waveform.

3. The combination of claim 2 wherein said portions of the continuous signal are amplitude clipped components of the sinusoidal waveform 4. The combination of claim 3 including bias means for varying the conduction angle of the continuous signal from which each of said signal portions is clipped.

5. The combination of claim 4 wherein said selectively controlled means includes phase shifting means for inverting at least one of said signal portions, and a switching control device interconnected with the signal clipping means and the phase shifting means for algebraically adding selected inphase signal portions from the signal clipping means and signal portions inverted by the phase shifting means.

6. The combination of claim 5 wherein said generating means includes at least one resonant feedback oscillator and control means connected to the oscillator for changing the frequency of the continuous signal.

7. The combination of claim 1 including bias means for varying the phase of the continuous signal from which each of said signal portions is clipped.

8. The combination of claim 1 wherein said selectively controlled means includes phase shifting means for inverting at least one of said signal portions, and a switching control device interconnected with the signal clipping means and the phase shifting means for algebraically adding selected in phase signal portions from the signal clipping means and signal portions inverted by the phase shifting means.

9. The combination of claim ll wherein said generating means includes at least one resonant feedback oscillator and control means connected to the oscillator for changing the frequency of the continuous signal.

10. The combination of claim 1 wherein said generating means includes an audiofrequency oscillator having a sinusoidal waveform output.

11. The combination of claim 10 wherein said selectively controlled means includes phase shifting means for inverting the signal portions, attenuating means connected to the signal clipping means for varying the gain of selected signal portions transmitted through the phase shifting means and in bypass relation thereto, switch means connected to the attenuating means and the phase shifting means for selecting the signal portions regulated by the attenuating means, and means for algebraically adding the selected signal portions transmitted through and bypassing the phase shifting means to produce said resultant signals.

12. The combination of claim 11 wherein said resultant signals simulate the tones of different musical instruments.

13. The combination of claim 1 wherein said selectively controlled means includes phase shifting means for inverting the signal portions, attenuating means connected to the signal clipping means for varying the gain of selected signal portions transmitted through the phase shifting means and in bypass relation thereto, switch means connected to the attenuating means and the phase shifting means for selecting the signal portions regulated by the attenuating means, and means for algebraically adding the selected signal portions transmitted through and bypassing the phase shifting means to produce said resultant signals.

14. The combination of claim 1 wherein said resultant signals simulate the tones of different musical instruments.

15. The combination of claim 14 including vibrato means for varying the phase of the continuous signal from which each of said signal portions is clipped.

16. In combination with a source of voltage, an audiofrequency oscillator connected to said source and having a sinusoidal waveform output, a clipping circuit network connected to said oscillator establishing a plurality of signal transmitting paths through which clipped signal portions of said output are conducted, bias control means connected to the source for establishing signal levels at which the output is clipped, a selector switch assembly connected to the clipping circuit network and the bias control means for selecting at least two of the signal transmitting paths, and a phase inverting circuit connected to the switch assembly for combining at least two of the clipped portions of the output conducted through the selected signal transmitting paths in phase shifted relation to each other.

17. The combination of claim 16'wherein the clipping circuit network includes a pair of clipping diodes and a-signal transmitting resistor connected in parallel to the oscillator to establish said signal transmitting paths, said bias control means being connected in shunt relation to the clipping diodes. i

18. The combination of claim 17 wherein said oscillator includes a current control device having input, output and control terminals, a regenerative feedback circuit interconnecting portions are clipped.

19. The combination of claim 18 including vibrato producing means connected to the bias means for cyclically varying the phases of the clipped signal portions.

20. The combination of claim 16 wherein said oscillator includes a current control device having input, output and control terminals, a regenerative feedback circuit interconnecting the output and control terminals for sustaining the sinusoidal output at a predetermined frequency, frequency control means connected to the feedback circuit for selecting said frequency, and bias means connected to the control electrode for establishing the phases of the output from which the signal portions are clipped.

21. The combination of claim 20 including vibrato producing means connected to the bias means for cyclically varying the phases of the clipped signal portions. 

1. A signal producing apparatus comprising means for generating a continuous signal, signal clipping means connected to said generating means for dividing the continuous signal into separate signal portions, and selectively controlled means connected to the signal clipping means for recombining different combinations of said signal portions establishing resultant signals which are different from the continuous signal.
 2. The combination of claim 1 wherein said continuous signal is a sinusoidal waveform.
 3. The combination of claim 2 wherein said portions of the continuous signal are amplitude clipped components of the sinusoidal waveform
 4. The combination of claim 3 including bias means for varying the conduction angle of the continuous signal from which each of said signal portions is clipped.
 5. The combination of claim 4 wherein said selectively controlled means includes phase shifting means for inverting at least one of said signal portions, and a switching control device interconnected with the signal clipping means and the phase shifting means for algebraically adding selected in-phase signal portions from the signal clipping means and signal portions inverted by the phase shifting means.
 6. The combination of claim 5 wherein said generating means includes at least one resonant feedback oscillator and control means connected to the oscillator for changing the frequency of the continuous signal.
 7. The combination of claim 1 including bias means for varying the phase of the continuous signal from which each of said signal portions is clipped.
 8. The combination of claim 1 wherein said selectively Controlled means includes phase shifting means for inverting at least one of said signal portions, and a switching control device interconnected with the signal clipping means and the phase shifting means for algebraically adding selected in phase signal portions from the signal clipping means and signal portions inverted by the phase shifting means.
 9. The combination of claim 1 wherein said generating means includes at least one resonant feedback oscillator and control means connected to the oscillator for changing the frequency of the continuous signal.
 10. The combination of claim 1 wherein said generating means includes an audiofrequency oscillator having a sinusoidal waveform output.
 11. The combination of claim 10 wherein said selectively controlled means includes phase shifting means for inverting the signal portions, attenuating means connected to the signal clipping means for varying the gain of selected signal portions transmitted through the phase shifting means and in bypass relation thereto, switch means connected to the attenuating means and the phase shifting means for selecting the signal portions regulated by the attenuating means, and means for algebraically adding the selected signal portions transmitted through and bypassing the phase shifting means to produce said resultant signals.
 12. The combination of claim 11 wherein said resultant signals simulate the tones of different musical instruments.
 13. The combination of claim 1 wherein said selectively controlled means includes phase shifting means for inverting the signal portions, attenuating means connected to the signal clipping means for varying the gain of selected signal portions transmitted through the phase shifting means and in bypass relation thereto, switch means connected to the attenuating means and the phase shifting means for selecting the signal portions regulated by the attenuating means, and means for algebraically adding the selected signal portions transmitted through and bypassing the phase shifting means to produce said resultant signals.
 14. The combination of claim 1 wherein said resultant signals simulate the tones of different musical instruments.
 15. The combination of claim 14 including vibrato means for varying the phase of the continuous signal from which each of said signal portions is clipped.
 16. In combination with a source of voltage, an audiofrequency oscillator connected to said source and having a sinusoidal waveform output, a clipping circuit network connected to said oscillator establishing a plurality of signal transmitting paths through which clipped signal portions of said output are conducted, bias control means connected to the source for establishing signal levels at which the output is clipped, a selector switch assembly connected to the clipping circuit network and the bias control means for selecting at least two of the signal transmitting paths, and a phase inverting circuit connected to the switch assembly for combining at least two of the clipped portions of the output conducted through the selected signal transmitting paths in phase shifted relation to each other.
 17. The combination of claim 16 wherein the clipping circuit network includes a pair of clipping diodes and a signal transmitting resistor connected in parallel to the oscillator to establish said signal transmitting paths, said bias control means being connected in shunt relation to the clipping diodes.
 18. The combination of claim 17 wherein said oscillator includes a current control device having input, output and control terminals, a regenerative feedback circuit interconnecting the output and control terminals for sustaining the sinusoidal output at a predetermined frequency, frequency control means connected to the feedback circuit for selecting said frequency, and bias means connected to the control electrode for establishing the phases of the output from which the signal portions are clipped.
 19. The combination of claim 18 including vibrato producing means connected to the bias means for cyclically varying the phases of the clipped signal portions.
 20. The combination of claim 16 wherein said oscillator includes a current control device having input, output and control terminals, a regenerative feedback circuit interconnecting the output and control terminals for sustaining the sinusoidal output at a predetermined frequency, frequency control means connected to the feedback circuit for selecting said frequency, and bias means connected to the control electrode for establishing the phases of the output from which the signal portions are clipped.
 21. The combination of claim 20 including vibrato producing means connected to the bias means for cyclically varying the phases of the clipped signal portions. 